Analytical ultracentrifuge cell



Jan. 6, 1970 D. H. MOORE 3,4 7,994

ANALYTICAL ULTRACENTRIFUGE CELL Original Filed Aug. 24, 1967 I0 I? No.

United States Patent O 3,487,994 ANALYTICAL ULTRACENTRIFUGE CELL Dan H.Moore, Cherry Hill, N.J., assignor to Canal Industrial Corporation, acorporation of Maryland Continuation of application Ser. No. 663,150,Aug. 24, 1967. This application May 8, 1968, Ser. No. 727,752 Int. Cl.B04b 9/12, 9/14 US. Cl. 233-26 4 Claims ABSTRACT OF THE DISCLOSURE Anultracentrifuge rotor assembly comprises a rotatable centrifuge head inwhich are mounted a plurality of bucket-type specimen analytical cellswith transparent windows each having a specimen-containing cavity and aplurality of transversely extending shoulders symmetrically disposedabout the axis of the cell. Each of the cells is supported in the headby a resilient pin and the head has a plurality of supporting socketseach disposed to be engaged by the shoulders of one of the cells and tosupport it radially during normal operation. The flexible supporting pinis deflected during normal operation by the centrifugal force acting onthe pin and, when the ultracentrifuge is stopped for removal of thecell, the pin retracts it from the head socket and permits it to swinginto a vertical position for removal. The analytical cell comprises anintegral metal body having a specimenreceiving cavity and connectingrecesses of larger areas in the upper and lower faces thereof and atransparent window secured by an epoxy resin adhesive in each of therecesses to form a single unitary structure. The vertical walls of thecell cavity lie substantially in radial planes during normal operationof the cell and the cell body has a plurality of transversely extendingshoulders symmetrically disposed about the axis. a

RELATED APPLICATION This application is a continuation of applicantsprior application Ser. No. 663,150, filed Aug. 24, 1967, now abandoned.

BACKGROUND OF THE INVENTION Ultracentrifugation can be divided into twomain categories:

(1) Preparative.

(2) Analytical.

Preparative ultracentrifugation generally makes use of one or the otherof two types of rotating heads:

1) Angle-in which the specimen cells are tubular and make a fixed anglewith the axis of rotation.

(2) Swinging bucket-4n which the specimen cells are tubes which hangvertically when the rotor head is at rest and swing out horizontallywhen the head reaches operating speed.

Such tubular cells of both the angle and swinging bucket types generallyhave a relatively large volume capacity, of the order of 15 to 200 cc.but, because of the centrifugal stresses on the angle cell or on thepivotal support of the swinging bucket, heads including large cellsgenerally must be operated at relatively lower centrifugal fields.

Preparative ultracentrifugation is used to separate colloidal substanceswith different densities or frictional coefficients for further analysisor examination. This separation may be made in solvents of uniformdensity or in solutions with a gradient in density from top to bottom.Gradient centrifugation is better served by swinging bucket rotor heads.

At present, preparative operations are carried out in the dark since theoperator is not able to determine what is taking place in the sampletube until the centrifuge is stopped and the specimen cell removed.During this manipulation, the distribution of components in the cell maybe altered. Also, centri'fugation may have been too short or too long togive a desired distribution or separation.

Analytical ultracentrifugation, on the other hand, requires specialcells with radial walls to prevent convection and transparent windowsand an optical system for viewing and photographing the contents of thecell while the head is rotating. Heretofore, analytical cells havealways been fixed in the rotating head with the top toward the axis ofrotation and the bottom toward the periphery. Usually, such cells have alow volume capacity, less than 1 cc., and have involved a complexconstruction consisting of many parts which must be taken apart forcleaning after each use and reassembled and reinstalled in the head forsubsequent use. Such cells have the disadvantage that it is generallynecessary to install them in the head and remove them from the head in ahorizontal position which permits a certain amount of mixing of the cellcontents both before and after centrifugation.

For a more detailed discussion of various ultracentrifugation processesand of standard equipments available, see the article Centrifugation byapplicant in Medical Physics, Vol. II, Otto Glasser, Editor, Year BookPublishers, Inc., Chicago, 1950, pp. 172-183.

It is an object of the invention, therefore, to provide a new andimproved rotor assembly for an ultracentrifuge capable of use for eitherpreparative or analytical ultracentrifugation, combining theabove-described advantages of both types.

SUMMARY OF THE INVENTION In accordance with the invention, there isprovided a swinging bucket-type analytical ultracentrifuge cell whichcomprises an integral metal body having a specimenreceiving cavity andconnecting recesses of larger areas in the upper and lower faces thereofand a transparent window secured in each of such recesses to form asingle unitary structure.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription, taken in connection with the accompanying drawing, whileits scope will be pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWING Referring to the drawing:

FIG. 1 is a perspective view of an ultracentrifuge head embodying theinvention, at rest;

FIG. 2 is a fragmentary cross-sectional view of a head showing aspecimen cell substantially in the position occupied during normaloperation, while FIG. 3 is a side elevation of the specimen cell shownin FIGS. 1 and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION Referring nowmore specifically to the drawing, there is shown a rotor assembly for anultracentrifuge comprising a rotatable supporting ultracentrifuge head10. The supporting and driving mechanism for the head comprises no partof the present invention and is, therefore, not shown. It may, forexample, be of the type described and claimed in the copendingapplication of applicant and John U. White, Ser. No. 480,407, filed Aug.17, 1965, and assigned to the same .assignee as the present application.The rotor assembly also includes a plurality of bucket-type specimencells 11, each of which, as

shown more clearly in FIG. 2, has a specimen-containing cavity 12 and acircular transversely extending shoulder 11a, 11a or a plurality ofindividual shoulders symmetrically disposed about the longitudinal axisof the cell 11.

As shown more clearly in FIG. 2, the vertical walls of each of the cellcavities lie substantially in radial planes of the rotor head duringnormal operation when centrifugal force swings the bucket-type cellsoutwardly into a substantially horizontal positon. The upper and lowerwalls of each of the cell cavities 12 is in the form of a transparentwindow, such as the windows 13 and 14 cemented into cavities in theupper and lower faces of the cell 11 with a suitable adhesive such as anepoxy resin. The term transparent, as applied to the windows 13 and 14,is used to indicate that they have a high transmissivity toelectromagnetic radiation in that portion of the spectrum used foranalyzing the contents of an ultracentrifuge cell, specificallyincluding any desired portion or all of the range from infrared toultraviolet, depending upon the application. Before the windows 13, 14are cemented into place, the metal parts are preferably anodized orotherwise suitably treated or coated to prevent chemical reaction withthe fluids under study. A resilient pin 15 supports each of the cells 11from the head, for example, the pin passes through extending lugs 11b,11b of the cell and through an oversize hole 16a in a lug 16 projectingfrom the frame of the head into a socket 17. The pin 15 may be retainedin place in any suitable fashion. As shown, the pin 15 extends throughthe walls of the socket 17, being threaded into one wall thereof. Thecell 11 is provided with a hole 18 through its upper wall for fillingthe cavity 12 and extracting the specimen therefrom. This hole is closedby a screw plug 19 and a sealing gasket 20. The hole 18 is preferablyrelatively large to permit easy access to the inside of the cell forcleaning.

The head is formed with a plurality of supporting sockets, such as thesocket 17, in which the upper ends of the cells 11 are disposed when thehead is at rest and each having surfaces disposed to be engaged by theshoulders of one of the cells 11 and to support the same radially duringnormal operation upon deflection of its associated pivot pin bycentrifugal force acting upon the cell. Specifically referring to FIG.2, the shoulders 11a, 11a of the cell 11, during normal operation, areforced to the right until they engage the surfaces 17a, 17a of thesocket 17, although these abutting surfaces are shown slightly separatedin the drawing for the sake of clarity.

It is believed that the operation of the ultracentrifuge rotor assemblywill be apparent from the foregoing description. In brief, when therotor head is at rest, the cells 11 all swing vertically downwardlyabout their respective pivot pins 15, as shown in FIG. 1. As the rotorhead is brought up to speed, the specimen cells 11 swing upwardly intothe horizontal position, as shown in FIG. 2, and, at normal operatingspeed, the centrifugal force acting on the cells is sufiicient to forcethem outwardly up to speed and after it reaches its final operatingspeed. During this period, the sedimentation of a-colloid in a densitygradient in a cell 11 can be observed while the redistribution isactually taking place. Such observations are important, both practicallyand theoretically. Furthermore, absorption, Schlieren, interference, orother optical systems can be used to observe or record the distributionof components at all times during the centrifugation process. At the endof a run, the resilient pin 15 retracts the cell 11 from engagement withthe surfaces 17a, 17a of the head socket and the cell gently andgradually swings to the vertical position so that the separatedfractions of the specimen in the cell can be removed undisturbed forfurther study. 1

This cell can also be used' for makinga synthetic boundary as describedby G. Kegeles (Jour. Amer. Chem. Soc. 74:5532, 1952) and by E. G.Pickels et al. (Proc. Nat. Acad. Sci. U.S. 381943, 1952) and by Vinogradet al. (Proc. Nat. Acad. Sci. U.S. 49:902, 1963). However, with the typeof analytical cell embodied in the present invention, most layers can beprepared before the cell is connected to the rotor head because bothgravity and centrifugal force is always directed toward the bottom ofthe cell as a result of its free swinging action. This cell, althoughconstructed of very few pieces, can be shaped to accommodate most of theprocesses accommodated by previous analytical cells, such as the longradial length double-channel cell of H. K. Schachman(Ultracentrifugation in Biochemistry, pp. 178-180, Academic Press, NewYork, 1959).

Thus, the ultracentrifuge rotor assembly embodying the invention isuseful both for preparative or analytical processes and the rotor head10 can be made much lighter than in the case of a rotor head including afixed standard analytical cell. This is because the cell constitutes thegreatest radius of the rotating head assembly. In the case of a. headwith a fixed analytical cell, the body of the head must extendconsiderably beyond and around the cell to support the very greatcentrifugal forces on the cell, thus significantly increasing its sizeand weight and the centrifugal forces which it must withstand.

What is claimed is:

1. A swinging bucket-type analytical ultracentrifuge cell comprising 'anintegral metal body having a specimen-receiving cavity and connectingrecesses of larger areas in the upper and lower faces thereof and atransparent window secured in each of said recesses to form a singleunitary structure.

2. An ultracentrifuge cell in accordance with claim 1 in which saidwindows are secured in said recesses by an epoxy resin adhesive.

3. An ultracentrifuge cell in accordance with claim 1 in which thevertical walls of said cell cavity lie substantially in radial planesduring normal operation of the cell.

4. An ultracentrifuge cell in accordance with claim 1 in which the cellbody has a plurality of transversely extending shoulders symmetricallydisposed about its' axis.

HENRY T. KLINKSIEK, Primary Examiner

